Rotating drum heat-treating furnace with internal fan



Aug. 4, 1959 E. G. DE CORIOLIS ROTATING DRUM HEAT-TREATING FURNACE WITHINTERNAL FAN Filed Nov. 7, 1956 2 Sheets-Sheet 1 K wm INVENTOR.

S u w m R m m C.m e/ d EM Y B 1959 E. G. DE CORIOLIS 2,898,099

ROTATING DRUM HEAT-TREATING FURNACE WITH INTERNAL FAN Filed Nov. 7, 19562 Sheets-Sheet 2 E G cle Comous BYW/% @TTORNEY 2,898,099 Patented Aug.4, 1959 ROTATING DRUM HEAT-TREATING FURNACE WITH INTERNAL FAN Ernest G.de Coriolis, Toledo, Ohio, assignor to Surface Combustion Corporation,Toledo, Ohio, a corporation of Ohio Application November 7, 1956, SerialNo. 620,917 Claims. (01. 263-34) This invention relates to theheat-treatment of articles and more particularly'to the circulation of agaseous atmosphere through small articles to be heat-treated that arelocated in a rotary conveyer.

The art of heat-treating, especially carburizing, small articles in acontinuous atmosphere furnace has proven difiicult. A suitable conveyorfor transporting the small parts through the furnace in large quantitieswhile uniformly exposing them to the heat-treating atmosphere has beenthe principal obstacle in this art. This ob- 'stacle has beensubstantially overcome by the rotary drum conveyor of Patent 2,624,561,Heyn, assigned to applicants assignee. However, many small parts,particularly those of suchsize or shape that relatively smallinterstices are formed among them, are not uniformly exposed to theatmosphere with the result that some parts have greater case depths thanothers. It has been found that by oscillating the drum with a netforward rotation,

the parts receive more tumbling action and are more uniformly subjectedto the atmosphere. Even this is insuificient in some cases,-forinstance, where small rollers for roller bearings are carburized.

To obtain still greater uniformity in case depth, a novel rotary drum orretort has been developed which contains a fan and means for obtainingpositive circulation of the gases therein. The gaseous atmosphere ismore 1 fully circulated past and through the work with this invention toobtain the utmost possible exposure and uniformity in case depth.

For further consideration of what is novel and the invention refer tothe following portion of the specification,

the depending claims, and the accompanying drawing.

In the drawing:

Figure l is a cross-sectional view on line 1-1 of Fig ure .2 ofapparatus embodying the invention,

. Figure 2 is an end view of the apparatus on line 2--2 of Figure 1,

Figure 3 is a circuit diagram employed with the apparatus of Figures 1and 2, and

Figure 4 is a view of alternate apparatus to that shown in Figure 1.

According to Figure 1, a furnace 11 comprises wall means forming aheating chamber 12 and a charge vestibule 13. Chamber 12 is heated byhorizontal radiant tubes '14, placed above and below rotary drum orretort 15. The drum, of cast alloy, contains a helical wall 16 integraltherewith which extends from the charge end to discharge opening 17. Thewall forms a helical passage 18 through which the particles to beheat-treated are carried as the drum rotates. The articles are generallycharged into the drum to a depth equal to /2 to the height of wall 16depending on the size and shape of the articles and the quantity desiredto be heat-treated.

. The charge end of drum 15 has a vertical wall 20,

which encloses this end except for a central opening through which atube 21. extends. This is sealed to and supported by the charge end wallof the vestibule. A charging trough 22, which is preferably of thevibratory type, carries articles placed thereon into the drum. Anasbestos or metal curtain 23 is located outside the vestibule chamber 13to cover the opening between tube 21 and trough 22 so as to maintain aminimum leakage of the atmosphere gas. Also, a flange 24 seals theopening between wall and tube 21.

A centrifugal or. radial flow fan 25 is located at the discharge end ofdrum 15 and has a shaft 26 extending outside the furnace to a sheave 27which is driven through a belt 28, sheave 30, and motor 31. The fan andshaft are supported by a first bearing 32 and a second bearing (notshown) located ina water cooled housing 33.

A tapered casing 34 connects bearing 32 to housing 33 to maintain properalignment of the bearings.

A cylindrical refractory bung 35 is sized to closely fit within theopening formed by drum 15 at the discharge end. The bung is held by ametal cylinder 36 which is indirectly affixed to buckstay 37 throughflange 38. A plate 39 is afiixed to this cylinder to support housing 33and casing 34. i

A tube or duct 40 is placed within the drum in the cylindrical spacedefined by the inner edge of helical wall 16. The duct thus makespassage 18 an enclosed one from the charge end of the duct to thedischarge end at hole 17. A smaller duct 41 extends from the duct 40 tothe central portion of fan 25 which is rotated in a counterclockwisedirection as viewed from the charge end of the furnace so as to impart asimilar motion to the gases drawn from ducts 40 and 41. The gaseswhirling in a counterclockwise direction then more easils enter duct 18,traveling therethrough until reaching the charge end of duct 40. Fromhere, they re-enter duct 40 and repeat the process. A portion of thegases leave the drum through port 17 and enter the chamber 12. However,additional atmosphere gas is emitted to the chamber 12 through inlet 42so that the pressure of the gas in the chamber soon equals that in thedrum and this leakage is reduced to a minimum. Additional gas is alsosupplied drum 15 through inlet 43 to make up leakage through hole 17,through the opening above chute 22, and through the small annularopenings between the drum and the bung and between the drum and thefurnace wall.

Particularly when the gas atmosphere in chamber 12 and drum 15 is to beclosely controlled, a wall 53 is fabricated around the drum and itsmechanism at the discharge end. The chamber is gas-tightly constructedand additional gas may be admitted to pressurize it and prevent outwardleakage of the furnace atmosphere gas through the aforementioned annularopenings.

The drum is rotated through a sprocket 44 attached to its peripheryoutside the discharge end of the furnace. The sprocket enmeshes a chain45 powered by a sprocket 46 and motor 47. The drum is supported at itsdischarge end by discs 48 co-acting with ring 50. At the change end, thedrum rests on rollers 51 whose shafts 52 extend outside the charge endwhere they are rotatably supported.

According to Figure 4, the gases may be circulated from the fan throughdrum 15 and back through the chamber to that portion of the retortadjacent the fan. In this case, a series of holes 71 are provided inwall 20 and another series of holes 72 are provided at the discharge endof the drum. The centrifugal or radial flow fan is preferably replacedby an axial flow fan 73. The ducts 40 and 41 are eliminated in this casealso, although a solid plug may be substituted therefor, if desried, toassure better flow of the gas through passage 18. The drive apparatushas been deleted from this View as it is similar to that of Figure 1.

'As previously mentioned, the work is more evenly subjected to theatmosphere if the drum is oscillated with a net advance. The parts areeffectively tumbled in this manner thus being subjected more uniformlyto the atmosphere. To accomplish this oscillation, motor 47 isreversible, having a forward winding 54 and a reverse winding 55.Current is supplied to winding 54 througha line 56, and to Winding 55through a line 57; line 58 is a common ground. Line 60 supplies currentto line 56 or 57 as regulated by a timer 61. This is a commerciallyavailable device that has two adjustable timing periods, one forregulating the length of time the drum rotates in the forward directionand one for the rearward direction. The degree of rotation depends, ofcourse, on the time the drum rotates and this time, depends mainly onthe characteristics of the parts to be treated and the depth to whichthey are charged in the drum. For small parts that closely pack, agreater degree of oscillation is required than for larger parts that donot closely pack and thus have large interstices among them. The degreeof forward rotation generally is between 60 and 160.

In a typical example, bearing rollers are to be carburized with surfacecarbon of 1.00% and with 0.40% carbon content to a depth of .050 inch.They are placed in the bottom of the drum to a depth of 6", the drumhaving 10 flights between the charge end and the discharge hole, thusrequiring 10 revolutions to transport the rollers through the furnace.With a given carburizing atmosphere at 1700 F., 8 hours are required inthe furnace for the rollers to attain the desired case and the drum mustmake a net advance of 1 A revolutions per hour. Further, assumingthe'drum rotates at a speed of revolutions per hour and a forwardrotation of 90 is necessary to effectively tumble the parts, then thedegree of rearward rotation may be found by the following formula:

where:

T=Total time in furnace, minutes N =Total number of revolutions requiredX: Number of degrees of forward rotation Y=Number of degrees of reverserotation S=Speed of drum, degrees per minute direction and 79.4 in arearward direction with a net forward advance of 10.5 This providesproper time in the furnace and ample tumbling action.

The invention thus provides means for recirculating atmosphere gaswithin a furnace and by the work to obtain maximum exposure of the workto the atmosphere. By recirculating the atmosphere gas, maximum use ofthe gas is thereby attained. Also, by recirculating the gas within thechamber, the temperature of the gas is maintained at an elevated amountand no heat loss occurs such as would happen if the gas wererecirculated through a duct outside said chamber. By both oscillatingthe drum and tumbling the work, exposure of the Work to the atmospheregas is even more uniform.

The foregoing illustrates the best mode of carrying out the invention,the scope of which is limited only by the depending claims.

I claim:

1. An atmosphere furnace comprising: wall means defining a heatingchamber having first and second aligned openings; a drum having alongitudinal axis containing a helical wall which forms an unobstructedhelical channel,.said drum having an open end; a wall gas-tightly 4aflixed to the other end of said drum and having a hole in the centralportion thereof; means for rotatably supporting said drum in saidchamber with said hole aligned with said first opening and with saidopen end extending through said second opening; means for substantiallycontinuously rotating said drum about its axis whereby to cause saidhelical wall to. advance work, charged into the drum through the firstopening, through said drum along said helical channel, a bung extendinginto said open end and afiixed to a support outside said chamber, saidbung being in close relationship to said open end; a fan located in saiddrum adjacent said open end and whose plane of rotation is perpendicularto the axis of said drum; a shaft connected to said fan and extendingoutwardly through said bung; bearing means supported by said bung forrotatably supporting said shaft; and means for rotating said shaft.

2. An atmosphere furnace comprising: wall means defining a heatingchamber having first and second aligned openings; a drum having alongitudinal axis containing a helical wall which forms an unobstructedhelical channel, said drum having an open end; a wall gas-tightlyaffixed to the other end of said drum and having a hole in the centralportion thereof; means for rotatably supporting said drum in saidchamber with said hole aligned with said first opening and with saidopen end extending through said second opening; a bung extending intosaid open end and affixed to a support outside said chamber, said bungbeing in close relationship to said open end; a fan located in said drumadjacent said open end and whose plane of rotation is perpendicular tothe axis of said drum; a shaft connected to said fan and rotatablysupported by said bung; means for rotating said shaft; a discharge holelocated in the periphery of said drum intermediate said fan and saidother end; and means for substantially continuously rotating said drumabout its axis whereby to cause work therein, charged into said drumthrough said hole, to advance through said drum along said helicalchannel to said discharge hole.

3. Carburizing apparatus comprising: wall means forming a heatingchamber having first and second openings in opposite ends thereof, saidfirst opening having a charging chute extending therethrough; anelongated drum rotatably supported in said chamber, one end of said drumhaving a centrally located opening adjacent said first opening andthrough which said chute extends, the other end being tapered to asmaller diameter and extending through said second opening in closefitting, rotatable relationship thereto; a fan in said drum adjacentsaid tapered end for recirculating gases in said drum; a shaft extendingoutwardly through said tapered end and being connected to said fan;means outside said drum for rotating said shaft; a stationary bungsupported outside said drum and extending into said tapered end in closefitting relationship thereto, said bung rotatably supporting said shaft;a helical passage in said drum formed by a helical wall therein; and acylindrical tube concentrically located in said drum, said tube havingone end adjacent the central portion of said fan and the other endterminating a substantial distance toward said other end of said drum.

4. In a carburizing furnace having a substantially gastight chamber, arotatable drum located in said chamber having an open end which extendsoutwardly through a Wall of said chamber, said drum containing a helicalwall which forms an unobstructed helical channel, means for rotatablysupporting said drum, and means including a reversible motor locatedoutside said chamber for rotating said drum, a fan adapted to be locatedin said drum adjacent said end and whose plane of rotation isperpendicular to the axis of said drum; a shaft connecting said fan andextending outside said end; means for rotating said shaft; and controlmeans for said motor for controlling the period of time in which thedrum is rotated in opposite directions, the period in one directionbeing longer the opposite in said drum.

5. In a heat treating furnace having a chamber, a rotatable drum locatedin said chamber, one end of which extends outwardly fromthe chamber,said drum containing a helical wall which forms an unobstructed helicalchannel, means for rotatably supporting said drum in said chamber, and areversible motor for rotating said drum, a fan adapted to be located insaid drum adjacent said end and whose plane of rotation is perpendicularto the x axis of said drum; a shaft connecting said fan and extendingoutside said end; means forrotating said shaft; and :control meansforreversing said motor at predetermined intervals.

6. In a carburizing furnace having a substantially gastight chamber, thecombination of a rotatable drum located in said chamber having an openend which extends outwardly through a wall of said chamber, said drumcontaining a helical wall which forms an unobstructed helical channel,means for rotatably supporting said drum, means including a reversiblemotor for rotating said drum, and control means for controlling theperiod of time in which the drum is rotated in opposite directions, theperiod in one direction being longer than the opposite direction, a fanadapted to be located in said drum adjacent said open end and whoseplane of rotation is perpendicular to the axis of said drum; a shaftconnecting said fan and extending outside said end; means for supportingsaid shaft independently of said drum; and means outside said drum forrotating said shaft.

7. In a heat-treating furnace having a heating chamber and a rotatabledrum located therein, said drum containing a helical wall in contactwith the inner surface thereof and whose height is less than the radiusof said drum, the improvement which comprises: a tube adapted to beaxially located in said drum within the space defined by the'inner edgeof the helical wall, and a fan within said drum and located at one endof said tube and aligned with said tube to recirculate gas through saidtube and drum.

8. In a heat-treating furnace having a heating chamber and a rotatabledrum located therein, said drum containing a helical wall in contactwith the inner surface thereof and whose height is less than the radiusof said drum, the improvement which comprises: a tube adapted to beaxially located in said drum within the space defined by the inner edgeof the helical wall, and a centrifugal fan whose central portion isadjacent one end of said tube whereby gas in said drum is circulatedfrom said fan through the passage formed by said Wall and said tube andback through said tube to said fan.

9. In a heat-treating furnace having a heating chamber and a rotatabledrum located therein, said drum containing a helical wall in contactwith the inner surface thereof and whose height is less than the radiusof said drum, the improvement which comprises: a tube adapted to beaxially located in said drum within the space defined by the inner edgeof the helical wall, said tube being substantially in contact with theinner edge throughout the length of said tube, whereby said tubesubstantially encloses a portion of the passage formed by the helicalwall; and a fan within said drum and located at one end of said tube forcreating a flow of gas through the enclosed passage.

10. In a heat-treating furnace having a heating chamber and a rotatabledrum located therein, said drum containing a helical wall in contactwith the inner surface thereof and whose height is less than the radiusof said drum, said drum having an opening in one end through which workto be heat-treated is charged, the improvement which comprises: a tubeadapted to be axially located in said drum within the space defined bythe inner edge of the helical wall, said tube being substantially incontact with the inner edge throughout the length of said tube, wherebysaid tube substantially encloses a portion of the passage formed bytheihelicalwall, a first'end of said tube terminating near the end ofsaid drum'opposite the end containing the opening, and the other end ofsaid tube terminating in said .drum toward the end containing theopening; and a fan Withinsaid drum located adjacent the first end ofsaid tube for creating a flow of gasthrough the enclosed passage'fromsaid fan toward the end of said drum containing the opening.

11. 'Apparatus for transporting work througha'heating chamber anduniformly subjecting said work to a gaseous atmosphere comprising: asubstantially horizontal rotatable drum; means for admitting gas to saiddrum; 2.

' charge opening at one end of said drum for receiving work to beheat-treated; a discharge opening near the other end of said drum; ahelical wall attached to the inner surface of said drum, said Wallforming a passage for carrying work from the charge opening to thedischarge opening when the drum is rotated, the height of said wallbeing less than the radius of said drum whereby the inner edge of saidwall defines a cylindrical space in the central portion of said drum; acylindrical tube located in said space, one end of said tube terminatingnear the discharge end of said drum and the other end of said tubeterminating in said space toward the charge end of said drum; and acentrifugal fan whose plane of rotation is substantially perpendicularto the axis of said drum and whose central portion is adjacent said oneend of said tube whereby gas in said drum flows through said passagetoward the charge end of said tube and returns through said tube whensaid fan is rotated.

12. Apparatus for transporting work through a heating chamber anduniformly subjecting said work to a [gaseous atmosphere comprising: asubstantially horizontal rotatable drum; means for admitting gas to saiddrum; a charge opening at one end of said drum for receiving work to beheat-treated; a discharge opening near the other end of said drum; ahelical wall attached to the inner surface of said drum, said wallforming a passage for carrying work from the charge opening to thedischarge opening when the drum is rotated, the height of said wallbeing less than the radius of said drum whereby the inner edge of saidwall defines a cylindrical space in the central portion of said drum;and a cylindrical tube located in said space, one end of said tubeterminating near the discharge end of said drum and the other end ofsaid tube terminating in said space toward the charge end of said drum.

13. A heat-treating furnace comprising: wall means defining a heatingchamber having a charge opening; a drum located in said chamber andhaving one end adjacent said opening and containing a hole through which'work is charged; means [for rotatably supporting said drum in saidchamber; an axial flow fan in said drum; drive means located outsidesaid chamber for rotating said fan independently of said drum; a firstport in said one end communicating with said chamber; a second port inthe other end adjacent said fan and communicating with said chamber,whereby gases are recirculated by said fan through said first port andback through said chamber to said second port. 7

14. Apparatus for transporting work through a heating chambercomprising: a substantially horizontal rotatable drum; a charge openingat one end of said drum for receiving work to be heat-treated; adischarge opening near the other end of said drum; a helical wallattached to the inner surface of said drum, said wall forming a passagefor carrying the work from the charge opening to the discharge openingwhen the drum is rotated, the height of said wall being less than theradius of said drum whereby the inner edge of said wall defines acylindrical space in the central portion of said drum; and a cylindricaltube located in said space, one end of said tube terminating near thedischarge end of said drum and the other end of said tube terminating inthe space toward the charge end of said drum.

15. An atmosphere furnace comprising: meansdefiningaheating chamberhaving first and second aligned openings and adi'scharge chute; adrumwhaving a longitudinal axis located in said chamber and aligned withsaid openings, one end of said drum defining a charge hole axiallyaligned 'with one of said openings for receiving Work to be charged intosaid drum; means for rotatably supporting said drum in said chamber; afan axially centered within and adjacent the other end of said drum andsupported through said other opening; drive means located outside saidchamber for rotating said fan independently of said drum; a portion ofsaid drum adjacent saidother end defining a discharge hole aligned withsaid discharge chute to diseharge' work thereinto as the drum rotates;and means for substantially continuously rotating said drum about itsaxis to advance work charged into the drum through said charge holethrough the drum to the discharge hole.

References Cited in the file of this patent UNITED STATES PATENTS1,358,313 Hero Nov. 9, 1920 1,824,747 DeCoriolis Sept. 22, 19312,624,561 Heyn Jan. 6, 1953 2,638,687 Vincent May 19, 1953 2,669,444Beetz Feb. 16, 1954 Maslin May 23, 1954

